interface CompurerAverage {

   public double average(double a,double b);

}

class A implements CompurerAverage {

   public double average(double a,double b) {

      double aver=0;

      aver=(a+b)/2;

      return aver;

   }

}

class B implements CompurerAverage {

   public double average(double a,double b) {

      double aver=0;

      aver=Math.sqrt(a*b);

      return aver;

   }

}

public class Example6_4 {

   public static void main(String args[]) {

      CompurerAverage computer;

      double a=11.23,b=22.78;

      computer = new A();  

      double result = computer.average(a,b);

      System.out.printf("%5.2f和%5.2f的算术平均值:%5.2f\n",a,b,result);

      computer = new B();  

      result= computer.average(a,b);

      System.out.printf("%5.2f和%5.2f的几何平均值:%5.2f",a,b,result);

   } 

}
